This invention relates to an abrasive product comprising polycrystalline self-bonded abrasive particles, and to a method of making such a product.
The production of leached self-bonded polycrystalline particles is taught in U.S. Pat. No. 4,776,861 in the name of General Electric Company. The method of this reference involves making a polycrystalline compact according to the teaching of, for example U.S. Pat. Nos. 3,141,746, 3,745,623, 3,767,371, 4,104,344, 3,609,818 and 4,224,380, size reducing the compact, e.g. by crushing, and leaching the non-particle matter such as solvent/catalyst from the bonded particles.
The leaching of the non-particle matter from the bonded particles becomes increasingly difficult as the grain size of the crystals making up the particles decreases, as the porosity of the self-bonded particles decreases, and as the size of the self-bonded particles increases.
The self-bonded particles produced according to the method of U.S. Pat. No. 4,776,861 are characterised by a large extent of diamond-to-diamond bonding, which results in a low friability (high strength), and a low porosity, usually less than about 10%.
Polycrystalline self-bonded diamond particles may also be produced using a shock wave method as taught in U.S. Pat. No. 3,238,019. The method involves non-diamond carbon being mixed with an inert material, and subjecting the mixture to an explosive shock wave in which very high pressures and high temperatures are realised for a short time period. The inert material is included in the mixture to facilitate heat removal from the system. The mixture is recovered from the explosion and crushed, before chemical treatment to remove remaining non-diamond carbon and the inert material. The cleaned diamond is then crushed further and graded as necessary.
Polycrystalline particles produced according to the method of U.S. Pat. No. 3,238,019 are characterised by a high friability (low strength) and very limited self-bonding.
U.S. Pat. No. 4,181,505 discloses a method of producing free discrete work-hardened diamond crystals. A large diamond is embedded in a mass of relatively large diamond crystals and this assembly subjected to temperature and pressure conditions at which diamond is thermodynamically stable. The large diamond crystal is work-hardened in this manner and is said to have shown evidence of plastic deformation.